Adding Circuits to an Electrical Panel

How do I add new circuits to my electrical breaker panel for new equipment that I will be installing? Evaluating the Electrical Load Capacity of a Panel, Identify Circuit Requirements.

Guide to Electrical Circuits and Panel LoadsElectrical Question: How do I add new circuits to my electrical breaker panel for new equipment that I will be installing?

I have a 2pole 40 amp circuit breaker supplying power to my shop. The panel in the shop has 4-15a.single pole breakers supplying power to 6-15a electrical outlets and 9-4 bulb florescent fixtures.

With these I also have1-2pole-15a. breaker for the heater and last but not least 1-2pole-20a breaker that is open for use.

How do I hook up a 220volt 12 amp table saw and a 220volt 15 amp joiner and staying with the 40amp 220volt supply into the shop coming from the house.

Anny Ideas?

This electrical wiring question came from: William, a Homeowner from Langley British Columbia, Canada.

Additional Comments: Very informative I am glad I found! Thank you.

Dave’s Reply:
Thanks for your electrical wiring question William.

How to Add Circuits to an Electrical Panel

Skill Level: Intermediate to Advanced – Best installed by a Licensed Electrician.
Tools Required: Basic Electricians Pouch Hand Tools, electric drill, auger bits and extension cord.
Estimated Time: Depends on personal level experience, ability to work with tools and install electrical circuit wiring.
Precaution: Identify the panel circuit, turn it OFF and Tag it with a Note before working with the wiring. Working in electrical panels is dangerous and not recommended for unqualified individuals.
Notice: Installing additional circuit wiring should be done according to electrical codes, with a permit, and all work should be inspected by the local building authority.

Electrical Circuits and Panel Loads for Your Home Workshop

Hi William, sure – I have some ideas and thoughts about this, let me break it down for you.

Evaluating the Electrical Load Capacity of a PanelWhat we need to understand is that just because there may be a lot of existing circuit breakers, this does not mean that everything will be used at the same time, especially if you are the only one that will be working in the shop.

Now there are some things that may be controlled automatically that you would need to consider.

Things like using a space heater on a cold day and the possibility that the space heater may come on at the same time as the table saw for example.

The main factor is to first understand the maximum allowable load or amperage that the panel is capable of providing, in this case it is 40 amps 240 volts.

Identify Full Load Requirements
Keep in mind that you do not want to load any circuit to the full capacity, in fact 80% circuit load is ideal.

Then make a list of all the existing circuit loads which would include the actual watts or amps of each the electrical devices.

Then really think about what items will be actually used at the same time. Now see what your available load capacity is.

Then you need to see if you have the physical space available to add more circuit breakers.

Keep in mind that your brand of panel may have twin circuit breakers or quad circuit breakers available which may create needed space, but this depends on the brand and type of panel that you have.

Here is an Electrical Tip for Workshops and Garages with Motorized Equipment

When possible, provide 220/240 volt power to equipment such as table saws, air compressors, etc.

Check to see if these types of equipment are dual voltage or 120/240 volts.

Understand that the motor connections will most likely need to be adjusted for the change in voltage and the receptacle and plug must be changed for the voltage and amperage as required.

The advantage is that the equipment will run much better and may be more efficient as well, which could actually save you on your electric bill because the electrical load will be closer to being balanced between the 240 volt power lines.

Basic Electrical Calculations Based on OHM’s Law

Electrical load calculations are as follows:

Watts equal the voltage times amperage.

Amps equal watts divided by the voltage.

NOTE: Remember to keep the circuit load below or at 80% of the circuit capacity.

Be Careful and Be Safe - Never Work on Energized Circuits!Consult your Local Building Department about Permits and Inspections for all Electric Wiring Projects.

Electrical Tip

The Safest Way to Test Electrical Devices and Identify Electric Wiring!

The Non-Contact Electrical Tester
This is a testing tool that I have had in my personal electrical tool pouch for years, and is the first test tool I grab to help identify electrical wiring. It is a Non-contact tester, [amazon.com], I use for the detection of Standard Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use.

Tom,
It all depends on what the circuit will be used for, the location, and the loads placed on the circuit. For example, you may install 10 receptacles in your garage on one 20 amp gfci circuit as long as the circuit will not become overloaded, ideally being loaded to 80% of the circuit capacity. The NEC Code specifies circuit requirements for specific rooms and equipment such as a dedicated gfci circuit which is required for bathroom receptacles. The kitchen has several codes related to circuit requirements as well. So circuit sizing always begins with the application and what the electrical code specifies for the circuit.
Dave